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From:   Aram Akhavan <github@aram.nubmail.ca>
To:     linux-nfs@vger.kernel.org
Cc:     Aram Akhavan <github@aram.nubmail.ca>
Subject: [PATCH 2/2] libnfsidmap: try to get the domain directly from hostname if the DNS lookup fails and always show the log message if the domain can't be determined
Date:   Mon, 12 Jun 2023 20:46:25 -0700
Message-Id: <20230613034625.498132-3-github@aram.nubmail.ca>
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In nfs4_init_name_mapping(), if no domain is specified in the config file, the hostname will be looked up in DNS, and the domain extracted from that.
If DNS resolution isn't up at this time (i.e. on idmapd startup), the hardcoded domain in IDMAPD_DEFAULT_DOMAIN is used. This will break id mapping
for anyone who doesn't happen to use "localdomain". Previously, the log message indicating this has happened requires -v to be passed, so the
"failure" was silent by default.

Signed-off-by: Aram Akhavan <github@aram.nubmail.ca>
---
 support/nfsidmap/libnfsidmap.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/support/nfsidmap/libnfsidmap.c b/support/nfsidmap/libnfsidmap.c
index 0a912e52..f8c36480 100644
--- a/support/nfsidmap/libnfsidmap.c
+++ b/support/nfsidmap/libnfsidmap.c
@@ -219,10 +219,15 @@ static int domain_from_dns(char **domain)
 
 	if (gethostname(hname, sizeof(hname)) == -1)
 		return -1;
-	if ((he = gethostbyname(hname)) == NULL)
-		return -1;
-	if ((c = strchr(he->h_name, '.')) == NULL || *++c == '\0')
-		return -1;
+	if ((he = gethostbyname(hname)) == NULL) {
+		IDMAP_LOG(1, ("libnfsidmap: DNS lookup of hostname failed. Attempting to use domain from hostname as is."));
+		if ((c = strchr(hname, '.')) == NULL || *++c == '\0')
+			return -1;
+	}
+	else {
+		if ((c = strchr(he->h_name, '.')) == NULL || *++c == '\0')
+			return -1;
+	}
 	/* 
 	 * Query DNS to see if the _nfsv4idmapdomain TXT record exists
 	 * If so use it... 
@@ -387,7 +392,7 @@ int nfs4_init_name_mapping(char *conffile)
 		dflt = 1;
 		ret = domain_from_dns(&default_domain);
 		if (ret) {
-			IDMAP_LOG(1, ("libnfsidmap: Unable to determine "
+			IDMAP_LOG(0, ("libnfsidmap: Unable to determine "
 				  "the NFSv4 domain; Using '%s' as the NFSv4 domain "
 				  "which means UIDs will be mapped to the 'Nobody-User' "
 				  "user defined in %s", 
-- 
2.39.2